Defibrotide for use in prophylaxis and/or treatment of graft versus host disease (gvhd)

ABSTRACT

Defibrotide for use in prophylaxis and/or treatment of Graft versus Host Disease (GVHD) in humans is disclosed, preferably in hematopoietic stem cell transplantation (HSCT), more preferably allogeneic hematopoietic stem cell transplantation. Graft versus Host Disease of the invention (GVHD) can be acute aGVHD and/or chronic cGVHD, preferably acute.

The present invention relates to defibrotide for use in prophylaxis and/or treatment of Graft versus Host Disease (GVHD) in humans, preferably in hematopoietic stem cell transplantation (HSCT), more preferably allogeneic hematopoetic stem cell transplantation. Graft versus Host Disease of the invention (GVHD) can be acute aGVHD and/or chronic cGVHD, preferably acute.

STATE OF THE ART

Graft versus Host Disease (GVHD) is the most frequent complication after allogenic haematopoietic stem cell transplantation (HSCT). GVHD can occur despite aggressive immunosuppressive prophylaxis even when the donor is a perfectly matched (HLA identical) sibling. It is a consequence of interactions between antigen presenting cell of recipient and mature-cell of donor.

Traditionally. GvHD is regarded as an epithelial cell disease. The three organs mainly involved in acute GvHD are skin, gastrointestinal tract and liver. All of them share the common feature of presenting a barrier to the ‘environment’ of the host. Chronic GvHD similarly attacks barrier tissues. In the chronic sicca syndrome of the eye, the oral, intestinal or genital mucosal compartments, as well as in bronchiolitis obliterans, the epithelial barrier of the mucosa is involved. Furthermore, GvHD is often considered as a single disease, split into two phases: an acute phase of GvHD occurring early after HSCT, and a chronic phase in which GvHD appears later in the course of transplantation.

Finally, in the traditional view, GvHD is cytokine-triggered. Damage induced by the conditioning preparative regimen used before transplantation and infections causes the release of diverse cytokines which are responsible for an inflammatory process, enhancing the GvHD reaction.

Defibrotide, a polydisperse mixture of single-stranded oligonucleotides, has a protective effect on activated endothelial cells. Preclinical studies revealed that defibrotide protects these cells against chemotherapy-induced cell death and activation, and downregulates the gene expression, protein level and activity of endothelial cell-triggers like heparanase. Defibrotide reduces procoagulant activity and increases fibrinolytic properties of stimulated endothelial cells without exacerbating systemic bleeding. Clinical studies of defibrotide in patients with severe hepatic Veno-Occlusive Disease (VOD) following HSCT have reported complete resolution in 36 to 50% of patients, and Day+100 survival in 35 to 42%. The prophylactic role of defibrotide has not been studied prospectively, but appears promising. We evaluated the efficacy and safety of defibrotide in preventing VOD against standard practice (no VOD prophylaxis) in a high-risk pediatric HSCT population.

Definition

The term defibrotide identifies a polydeoxyribonucleotide that is obtained by extraction from animal and/or vegetable tissues but which may also be produced synthetically; the polydeoxyribonucleotide is normally used in the form of an alkali-metal salt, generally a sodium salt, and generally has a molecular weight of 13 to 30 kDa (CAS Registry Number: 83712-60-1). Preferably, defibrotide is obtained according to U.S. Pat. Nos. 4,985,552 and 5,223,609 and/or presents the physical/chemical characteristics described in the same U.S. Pat. Nos. 4,985,552 and 5,223,609, herein incorporated by reference. More in particular, defibrotide is a mixture of polydeoxyribonucleotides having formula of random sequence:

P1-5,(dAP)₁₂₋₂₄,(dGp)₁₀₋₂₀,(dPp)₁₃₋₂₈,(dCp)₁₀₋₂₀

wherein P=phosphoric radical, dAp=deoxyadenylic monomer, dGp=deoxyguanylic monomer, dTp=deoxythymidinic monomer. dCp=deoxycytidynic monomer. and/or shows the following chemical/physical characteristics: Electrophoresis=homogeneous anodic mobility, and/or extinction coefficient, E₁ cm^(1%) at 260±1 nm nm=220±10, and/or E₂₃₀/E₂₀₀=0.45±0.04, and/or coefficient of molar extinction (referred to phosphorous) ε(P)=7.750±500, and/or rotatory power [α]_(D) ^(20°)=53°±6; and/or reversible hyperchromicity, indicated as % in native DNA and/or h=15±5.

The term humans identifies any subject as adult subjects and pediatric population, wherein with the term pediatric population is intended the part of population from birth to eighteen (18) years old.

The term aGVHD identifies acute Graft versus Host Disease;

The term cGVHD identifies chronic Graft versus Host Disease; and

The term allogenic referred to hematopoietic stem cell transplantation (HSCT) identifies transplant from an healthy subject to a (patient) recipient.

DESCRIPTION OF THE INVENTION

The present invention refers to defibrotide for use in prophylaxis and/or treatment of Graft versus Host Disease (GVHD) in humans, preferably in hematopoietic stem cell transplantation (HSCT). Graft versus Host Disease of the invention (GVHD) can be acute aGVHD and/or chronic cGVHD, preferably acute.

According to the invention, defibrotide can be administered to humans before and/or after hematopoietic stem cell transplantation (HSCT).

We have recently performed an international, randomized, controlled, open-label trial, wherein we compared defibrotide (Gentium S.p.A.) prophylaxis with no prophylaxis in pediatric HSCT patients at high risk for developing VOD. The primary endpoint was the incidence of VOD by Day+30 post-HSCT, adjudicated by a blinded, independent review committee. Secondary endpoints included graft-versus-host disease (GVHD), VOD-related organ failure and mortality.

A total of 356 patients met the inclusion criteria and gave informed consent to be randomized to the i.v. defibrotide arm (n=180) or the control arm (n=176). VOD was reported in 22 patients (12%) in the defibrotide arm and in 35 patients (20%) in the control arm (competing risk, P=0.05; Kaplan-Meier, P=0.05). The incidence and severity of acute GVHD were significantly reduced (P=0.005 and P=0.003, respectively) in the allogeneic recipients. VOD-associated organ failures were lower in the defibrotide arm with a significant reduction in the incidence of renal failure (1% vs. 6%, P=0.02). A significantly higher Day+100 mortality was observed in patients with VOD (25% vs. 6%; P<0.001). Although mortality after VOD diagnosis was lower in the defibrotide arm (4 vs. 10 patients, P=0.1), overall mortality was similar in the two arms. There was no difference in the incidence of adverse events between arms (87% vs. 88%).

Defibrotide reduced the incidence of VOD by 40%, as well as the incidence and severity of acute GVHD, and has a good safety profile. (ClinicalTrials.gov number, NCT00272948.)

Methods: Study Design

This study was a phase 3, multicenter, randomized trial, supported Gentium S.p.A. The study protocol and patient consent form were approved by the research ethics committees of the participating centers and written informed consent was obtained from patients and/or their legal representatives prior to study entry.

Treatment assignments were generated by a central data manager with a computer algorithm accessing a randomization sequence. Randomization was 1:1, stratified by center and the diagnosis of osteopetrosis. An independent data and safety monitoring board (DSMB) of three expert hematologists and a statistician reviewed the safety and mortality data at predetermined intervals. A blinded independent review committee (IRC) of three expert hematologists reviewed and adjudicated diagnosis for all suspected and documented VOD cases. An independent statistician performed the data analysis.

Eligible patients were aged <18 years with myeloablative conditioning for allogeneic or autologous HSCT, who had at least one risk factor for VOD: pre-existing liver disease, second myeloablative HSCT, allogeneic HSCT for leukemia beyond the second relapse, conditioning with busulfan and melphalan, previous treatment with GO, and diagnoses of inherited MAS, adrenoleukodystrophy, or osteopetrosis.

Treatment

For patients randomized to the open-label defibrotide arm, the study drug was administered daily at 25 mg per kilogram of body weight per day in four divided intravenous infusions. Defibrotide prophylaxis started on the some day as the pre-transplant conditioning regimen and was continued until Day+30 or, if discharged from hospital before Day+30, for a minimum of 14 days. Patients in the control arm received no prophylaxis against VOD.

Treatment with systemic t-PA, therapeutic-dose heparin or other antithrombotics was not permitted. Ursodiol was permitted.

Patients in either arm who developed VOD received treatment with defibrotide at 25 mg per kilogram per day until complete resolution of all symptoms or death.

Outcome Measures

The primary endpoint was the incidence of VOD by Day+30. VOD was assessed by the Investigator according to modified Seattle criteria, defined as the presence of two or more criteria: bilirubin >2 mg per deciliter (>34 μmol per liter), hepatomegaly, ascites, and/or unexplained weight gain >5% from baseline (modified from >2% weight gain in the original Seattle criteria²).

Laboratory parameters, including bilirubin, were measured at baseline (before conditioning) and at least weekly post transplant. AN patients underwent abdominal ultrasonography at baseline and after transplant, when VOD was clinically suspected, to confirm presence of hepatomegaly and ascites. The blinded ultrasound reports and clinical data were sent to the IRC for adjudication of suspected and diagnosed VOD cases. The IRC assessments were used in the primary efficacy analysis.

The secondary and exploratory efficacy parameters included:

(a) The incidence and severity of GVHD (international Bone Marrow Transplant Registry index) by Day+100 and Day+180. (b) MOF and mortality by Day+100; although this study was not powered to assess MOF or mortality, these endpoints were analyzed together using a composite scoring system for the assessment of VOD severity. This system assigned one point for each organ failure in patients with VOD: respiratory failure (oxygen requirement and/or ventilator dependence), renal failure (the doubling of baseline creatinine level and/or dialysis dependence) and encephalopathy; five points were assigned for death (regardless of cause of death). Patients without VOD were assigned zero. Each composite score component was also analyzed individually. (c) The incidence of transplant-associated microangiopathy (TAM)³¹ by Day+180.

Adverse events were recorded until Day+180 and coded using MedDRA terms.

Statistical Analysis

Analyses were performed as specified in the protocol and statistical analysis plan. The sample size was estimated based on the primary endpoint (VOD incidence by Day+30). VOD rates were estimated at 30% in the control arm and 15% In the defibrotide arm. Assuming a one-sided level of significance at 0.025, power of 80%, and a 10% dropout rate, 135 patients per arm were required. Because the incidence of VOD in children was unclear when the study was designed, the protocol incorporated a planned adaptive interim analysis, following the algorithm of Denne, to be reviewed by an independent DSMB when 120 patients per arm reached the Day+30 primary endpoint. The DSMB recommended to increase the sample size to a total of 360 randomized patients.

All data analyses were performed on the intent-to-treat (ITT) population, which included all patients with informed consent randomized into the study. Comparison against the defibrotide arm for the primary efficacy analysis was performed using a cumulative competing risk approach by Kalbfleisch and Prentice as discussed in Tai et al., where death not due to VOD, discontinuing the study due to an adverse event, and receipt of second transplant due to transplant failure, were considered competing risks. A supportive analysis was also performed using the log-rank test with Kaplan-Meier estimates of VOD rate, where patients not experiencing VOD were censored at Day+30, last known follow-up, or at the time of competing risk, whichever was earlier. A secondary per protocol (PP) analysis was also planned, excluding prematurely withdrawn ITT patients and ITT patients with serious protocol violations.

The secondary efficacy analyses on the incidence and severity of GVHD were analyzed using the Z-test for proportions and the two-sample Wilcoxon rank sum test, respectively. Patients with no GVHD were assigned a severity value of 0.

The analysis on the VOD composite score was performed using an exact Wicoxon's test with a two-sided 5% level of significance.

Each composite score component was analyzed using the chi-square test. Kaplan-Meier distributions of time to death by Day+100 for each study arm were compared using the log-rank test, where surviving patients were censored at Day+100 or last known follow-up, whichever was earlier.

The safety population was defined for the defibrotide arm as all recipients of at least one dose of study drug, and for the control arm as all assigned patients. Safety parameters were assessed using frequency tables for serious and non-serious adverse events (AEs), laboratory tests, and survival up to Day+180, where survival is defined as the time in days between HSCT and death from any cause.

Results: Patient Characteristics

Between January 2006 and January 2009, 360 patients were randomized to the study in 28 centers in 11 countries in Europe. In the defibrotide arm, 181 patients were randomized, one in error (without consent), resulting in 180 patients in the ITT population. In the control arm, 179 patients were randomized, three in error (without consent), resulting in 176 patients in the ITT population.

The mean age of the study population was 6.6 years. Patients were evenly distributed with respect to age and gender across the study arms (Table 1). The primary diseases, type of donor, type of graft, and incidence of risk factors for VOD were similar between arms.

Patients randomized to the defibrotide arm received study drug for a mean duration of 32.4 days (median, 35.0). When defibrotide was used for treatment of VOD, the mean duration of therapy was 28.7 days (median, 23.0) for the defibrotide arm and 21.7 days (median, 18.5) for the control arm. The number of patients using concomitant ursodiol was similar between arms.

VOD Incidence:

The incidence of VOD was reduced by 40% in the defibrotide arm compared with the control arm. Analysis of the ITT population showed a significantly lower incidence of VOD by Day+30 in the defibrotide arm versus the control arm (cumulative incidence, 12% vs. 20%, respectively, according to modified Seattle criteria; competing risk, P=0.05; Kaplan-Meier, P=0.05; Table 2). Analysis of the PP population also showed statistically significant results (competing risk, P=0.02; Kaplan Meier, P=0.02).

To explore consistency of results across different criteria, an additional subset analysis was performed applying Baltimore criteria, where bilirubin >2 mg per deciliter (>34 μmol per liter) is required for VOD diagnosis, with two of other three criteria, hepatomegaly, ascites or weight gain >5%. We identified fewer VOD cases with Baltimore criteria (7% in the defibrotide arm, 13% in the control arm; P=0.09; Table 2). While not significant, these data are consistent with the 40% reduction in VOD observed with modified Settle criteria.

Effect of Defibrotide on GVHD

The patients who received defibrotide prophylaxis experienced a significantly lower incidence and severity of aGVHD by Day+100. In allogeneic HSCT recipients from the ITT population, the incidence and severity (Grades 1 to 4) of aGVHD were significantly lower in the defibrotide arm than in the control arm (P=0.005 and P=0.003, respectively), even when Grade 1 aGVHD was excluded (Table 3). There was no difference in the incidence of chronic GVHD (cGVHD) by Day+180 between study arms.

Despite its protective effects against aGVHD, defibrotide did not interfere with the desirable graft versus leukemia effect. The combined Day+100 relapse rates of acute lymphoblastic leukemia, acute myeloid leukemia, other leukemias and myelodysplastic syndromes were 6% for the defibrotide arm versus 8% for the control arm, and combined Day+180 relapse rates were 7% and 10%, respectively.

VOD-Associated MOF and Death:

To assess the effects of defibrotide on the severity of VOD, a pre-specified composite scoring system was used to quantify VOD-associated MOF and death up to Day+100. Overall, the defibrotide arm had fewer VOD-associated organ failures and deaths, resulting in a statistically significant reduction of scores (Wilcoxon test, P=0.03) in the ITT population (Table 4). Specifically, the defibrotide arm showed a statistically significant lower incidence of renal failure compared with the control group (1% vs. 6%; P=0.02). Severe VOD-associated MOF by Day+100 was significantly higher in patients who fulfilled Baltimore criteria (60% vs. 32%; chi-square test, P=0.04).

VOD-associated mortality at Day+100 was lower in the defibrotide arm than the control arm (2% and 6%, respectively), but these results were not statistically significant (Table 4). Overall mortality was similar in the two arms when assessed at Day+100 and Day+180

Mortality was significantly higher in patients with VOD at Day+100 than in those without VOD (25% vs. 6%, respectively; P<0.0001).

Overall, most fatal AEs were in the categories “Neoplasms, Malignant and Unspecified” (7% and 8% in the defibrotide and control arms, respectively), and “Infections and Infestations” (3% and 6%, respectively).

TAM

There was no difference in the incidences of TAM (3% and 4% in the defibrotide and control arms, respectively) by Day+180.

Safety

The safety population included 177 patients of the defibrotide arm and all 176 patients in the control arm. The incidences of AEs (Table 5), and of serious adverse events (SAEs) and events leading to study discontinuation were similar between arms. A total of 207 SAEs were reported in 108 patients assigned to the defibrotide arm and 231 were reported in 103 control patients. Although the most common AE considered by the Investigator to be possibly, likely or certainly related to defibrotide was hemorrhage, the incidence of hemorrhage was similar between arms.

DISCUSSION

Although HSCT offers the only available cure for many diseases, the procedure remains limited by regimen-related toxicities, including GVD and hepatic VOD. Indeed, our results show a nearly four-fold higher mortality rate in patients with VOD compared with patients without VOD, and confirm previous observations.

In this study, prophylactic defibrotide reduced the incidence and severity of aGVHD. Damage to the endothelial cells of skin, gastrointestinal tract and liver from conditioning regimens contributes to the onset of aGVHD. Defibrotide's anti-inflammatory and protective effect on endothelial cells and down regulation of heparanase gene expression could explain these results, which appear highly consistent with the proposed mechanism of action of defibrotide.

Overall, defibrotide was well tolerated. Hemorrhages occurred with a similar frequency in both study arms, strongly suggesting that these events are more likely related to SCT and VOD than to the administration of defibrotide.

Object of the present invention is therefore defibrotide for use in prophylaxis and/or treatment of Graft versus Host Disease (GVHD) in humans, preferably in hematopoietic stem cell transplantation (HSCT), more preferably allogeneic hematopoietic stem cell transplantation. Graft versus Host Disease of the invention (GVHD) can be acute aGVHD and/or chronic cGVHD, preferably acute.

Defibrotide according to the invention can be administered before and/or after hematopoietic stem cell transplantation (HSCT), preferably before and/or after allogeneic hematopoietic stem cell transplantation.

Defibrotide according to the invention is preferably administered in a dose ranging from 10 to 60 mg/kg per day, preferably in a dose ranging from 20 to 40 mg/kg per day and more preferably in a dose of about 25 mg/kg per day; the kg refers to the body weight of the patient. According to the invention, defibrotide can be administered in a single or repeated dose/s per day, preferably in four (4) doses per day.

According to the invention defibrotide is preferably administered intravenously, more preferably is formulated in aqueous solution form.

REFERENCES

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TABLE 1 Baseline Demographics of the Study Participants. Defibrotide Control Arm Arm Variable (N = 180) (N = 176) Age-yr Mean (SD) 6.5 (5.2) 6.7 (5.4) Median 5.1 4.6 Range <1-18 <1-18 Age category-No. Infant and toddlers (28 46 (26) 41 (23) (%) days to 2 years) Children (>2 and ≤11 years) 91 (51) 95 (54) Adolescents (>11 years) 43 (24) 40 (23) Female gender- Female 70 (39) 75 (43) No. (%) Primary disease- Neuroblastoma 34 (19) 33 (19) No. (%) Acute myelogenous leukemia 31 (17) 42 (24) Acute lymphoblastic leukemia 26 (14) 22 (13) Other leukemia 8 (4) 5 (3) Myelodysplastic syndrome 20 (11) 11 (6)  Familial hemophagocytic 6 (3) 12 (7)  lymphohistiocytosis Other inherited MAS 4 (2) 3 (2) Soft tissue sarcoma 9 (5) 8 (5) Osteopetrosis* 7 (4) 6 (3) Adrenoleukodystrophy 1 (1) 1 (1) Other 34 (19) 33 (19) Type of donor- Matched related donor 35 (19) 25 (14) No. (%)† Matched unrelated donor 55 (31) 61 (35) Mis-matched related donor 14 (8)  10 (6)  Mis-matched unrelated donor 18 (10) 21 (12) Autologous HSCT 53 (29) 55 (31) Type of graft-No. Bone marrow 79 (44) 81 (46) (%)† Peripheral blood stem cells 74 (41) 77 (44) Umbilical cord blood 16 (9)  10 (6)  T-cell depleted stem cells 6 (3) 4 (2) Immuno- ATG-Horse 2 (1) 2 (1) suppression- ATG-Rabbit 65 (36) 80 (45) No. (%) Campath (alemtuzumab) 9 (5) 5 (3) Cyclosporine A 100 (56)  104 (59)  Methotrexate 56 (31) 65 (37) OKT-3 11 (6)  7 (4) Other‡ 31 (17) 28 (16) Conditioning Busulfan IV 80 (44) 81 (46) agent- Busulfan PO 46 (26) 44 (25) No. (%) Melphalan 126 (70)  114 (65)  Cyclophosphamide 84 (47) 80 (45) Etoposide 22 (12) 25 (14) Total Body Irradiation 17 (9)  18 (10) Fludarabine 34 (19) 40 (23) Treosulfan 13 (7)  13 (7)  Other§ 34 (19) 31 (18) VOD high risk Second myeloablative transplant 25 (14) 23 (13) criteria-No. (%) Allogeneic HSCT for leukemia 17 (9)  11 (6)  Pre-existing liver disease 41 (23) 54 (31) Prior abdominal irradiation 9 (5) 8 (5) Prior treatment with gemtuzumab 11 (6)  5 (3) Conditioning with busulfan and 106 (59)  99 (56) melphalan Osteopetrosis 7 (4) 6 (3) Inherited MAS 10 (6)  15 (9)  Adrenoleukodystrophy 1 (1) 1 (1) ATG denotes antithymocyte globulin, HSCT hematopoietic stem cell transplantation, MAS macrophage activation syndromes. *Osteopetrosis was a stratification fact †Five patients (3%) in the defibrotide arm and 4 patients (2%) in the control arm were without transplant data (did not proceed to myeloablative transplant or withdrew conditioning before transplant). ‡Other immunosuppressants: mycophenolate mofetil, tacrolimus sirolimus, antilymphocyte globulin, prednisone/steroids, m-PDN and rituximab, §Other conditioning agents-, thiotepa, alemtuzumab, ractioimmunoantibodym carboplatin, rituximab, ATG, clofarabine, Endoxan, dexamethasone, amsacrine, aracytabine, muromonab C and BCNU.

TABLE 2 Incidence of Veno-Occlusive Disease (VOD) Up To Day + 30 Post Hematopoietic Stem-Cell Transplantation (HSCT). VOD Diagnosis Defibrotide Arm Control Arm P value VOD by Day + 30/ VOD diagnosed-No./N 22/180 (12) 35/176 (20) IRC (ITT)* (%) Competing risk-% (95% 13 (8,19) 20 (15,27) 0.05 CI)† Kaplan-Meier-% (95% 13 (9,19) 20 (15,27) 0.05‡ CI) VOD by Day + 30/ VOD diagnosed-No./N 18/159 (11) 34/166 (20) IRC (PP)§ (%) Competing risk-% (95% 11 (7,17) 20 (15,28) 0.02 CI)† Kaplan-Meier-% (95% 11 (7, 18) 21 (15,28) 0.02‡ CI) VOD in patients 1/7 (14) 4/6 (67) with osteopetrosis- No./N (%)¶ VOD by type of Allogeneic HSCT 15 (8) 25 (14) donor-No. (%)* Autologous HSCT 7 (4) 10 (6) VOD diagnosis Weight gain > 5% 19 (11) 30 (17) criteria met- Ascites 17 (9) 26 (15) No. (%)* Hepatomegaly 19 (11) 30 (17) Increased bilirubin 13 (7) 22 (13) 0.09 VOD by Age Infants 9/46 (20) 11/41 (27) distribution Children 10/91 (11) 16/95 (17) No./N (%) Adolescents 3/43 (7) 8/40 (20) *Intent to treat (ITT) population, N = 180 defibrotide arm and N = 176 control arm. †Confidence interval (CI) by in transformation. ‡P value of log-rank test (from Kaplan-Meier estimator). §Per protocol (PP) population, N = 159 defibrotide arm and N = 166 control arm. ¶N denotes number of patients with osteopetrosis; N = 7 defibrotide arm and N = 6 control arm.

TABLE 3 The Incidence of Acute and Chronic Graft-Versus-Host disease (GVHD) in Allogeneic Hematopoietic Stem-Cell Transplantation (HSCT) Patients.* Defibrotide Arm Control Arm (N = 122) (N = 117) GVHD classification No. (%) No. (%) P value Acute GVHD by Day + 100 57 (47) 76 (65) 0.005† Acute GVHD severity Grade 1 30 (25) 33 (28) Grade 2 18 (15) 30 (26) 0.003‡ Grade 3 5 (4) Grade 4 4 (3) 4 (3) Grades 2 to 4¶ 27 (22) 43 (37) 0.01† Chronic-GVHD by Day + 180 16 (13) 17 (5)  0.8§ *In the ITT popuation of all patients (allogeneic and autologous HSCT patients), acute GVHD was present in 32% (57/180) of patients in the defibrotide arm and 43% (76/176) of patients in the control arm; P = 0.03. †P value from chi-square test for incidence of GVHD by Day + 100. ‡P value from Wilcoxon test for grading of GVHD by Day + 100. §P value from chi-square test for incidence of GVHD by Day + 180. ¶In a subset of grade 2 to 4 acute GVHD (excluding grade 1 mild cases), incidence as P = 0.01 and severity was P = 0.02 between the two arms.

TABLE 4 Veno-Occlusive Dase (VOD)-Associated Multiple Organ Failure and Death Up To Day + 100.* Defibrotide Arm Control Arm (N = 180) (N = 176) Event No. (%) No. (%) Respiratory failure 11 (6)  15 (9)  Renal failure 2 (1) 10 (6)  Encephalopathy 1 (1) 3 (2) Mortality 4 (2) 10 (6)  No organ failure or mortality 169 (94)  159 (90)  *Composite score in patients with VOD: 1 point for each organ failure; 5 points for mortality. Wilcoxon test for VOD-associated multiple organ failure and death in all patients at Day + 100: defibrotide arm versus control arm, P = 0.03. Wilcoxon test for VOD-associated multiple organ failure and death in patients with VOD at Day + 30: defibrotide arm versus control arm, P = 0.2.

TABLE 5 Patients with Drug-Related Adverse Events According to Treatment Arm by System Organ Class and Preferred Term.* Defibrotide Arm Control Arm† (N = 177) (N = 176) System Organ Class/Abnormality No. (%) No. (%) Blood and lymphatic system disorders Coagulopathy 0 (0) 1 (1) Gastrointestinal disorders Gastrointestinal hemorrhage 2 (1) 3 (2) Abdominal pain 1 (1) 0 (0) Diarrhea hemorrhagic 1 (1) 0 (0) Hematemesis 1 (1) 0 (0) Mouth hemorrhage 1 (1) 0 (0) Nausea 1 (1) 0 (0) Upper gastrointestinal hemorrhage 0 (0) 1 (1) Vomiting 1 (1) 0 (0) Investigations Activated partial thromboplastin time prolonged 0 (0) 2 (1) Prothrombin time prolonged 1 (1) 1 (1) Respiratory, thoracic, and mediastinal disorders Epistaxis 2 (1) 1 (1) Hemothorax 1 (1) 1 (1) Pulmonary hemorrhage 0 (0) 1 (1) Vascular disorders Hemorrhage 1 (1) 1 (1) Microangiopathy 0 (0) 1 (1) * Related adverse events are those classified by the investigator as possibly, likely or certainly related to study drug. †Adverse events reported following a diagnosis of veno-occlusive disease (VOD); defibrotide received as treatment for VOD. 

1. A method of preventing Veno-Occlusive Disease (VOD) comprising administering to a patient at risk of VOD an amount of defibrotide sufficient to reduce the occurrence or severity of VOD.
 2. The method of claim 1, wherein heparin or other antithrombotics are not administered to the patient.
 3. The method of claim 1, wherein the VOD is hepatic VOD.
 4. The method of claim 1, wherein the patient is a pediatric patient.
 5. The method of claim 1, wherein the administration of defibrotide occurs before the patient is subjected to hematopoietic stem cell transplantation (HSCT).
 6. The method of claim 1, wherein the administration of defibrotide occurs on the first day of a pre-transplant conditioning regimen.
 7. The method of claim 1, wherein the administration of defibrotide starts on the same day as a pre-transplant conditioning regimen.
 8. The method of claim 1, wherein the administration of defibrotide continues for at least 14 days.
 9. The method of claim 8, wherein the administration of defibrotide continues for at least 23 days.
 10. The method of claim 9, wherein the administration of defibrotide continues for at least 30 days.
 11. The method of claim 3, wherein the HSCT is an allogenic hematopoietic stem cell transplantation.
 12. The method of claim 1, wherein the defibrotide is administered in a dose ranging from 10 to 60 mg/kg/day.
 13. The method of claim 12, wherein the defibrotide is administered in a dose ranging from 20 to 40 mg/kg/day.
 14. The method of claim 13, wherein the defibrotide is administered in a dose of about 25 mg/kg/day.
 15. The method of claim 1, wherein the defibrotide is administered in a single dose.
 16. The method of claim 1, wherein the defibrotide is administered in repeated doses per day.
 17. The method of claim 16, wherein the defibrotide is administered in four doses per day.
 18. The method of claim 1, wherein the defibrotide is administered intravenously.
 19. The method of claim 1, wherein the defibrotide is administered in aqueous form.
 20. The method of claim 1, wherein the defibrotide was obtained by extraction from animal tissues.
 21. The method of claim 20, wherein the defibrotide was obtained by extraction from mammalian organs.
 22. The method of claim 1, wherein the patient is monitored at least weekly post-HSCT transplant.
 23. The method of claim 22, wherein the patient's bilirubin levels are measured.
 24. The method of claim 22, wherein the patient's abdominal ultrasound is measured. 